Advanced Air Cadets
Lesson 2 - Aircraft Systems and Electricity
Systems and Electricity
The Aircraft is very complex. In the design stage and in
the flight and maintenance manuals (used by pilot and
maintenance technicians) it is broken down into simpler
systems that carry out homogeneous functions. Some
examples include but are not limited to:
- Electrical
- Hydraulics
- Oxygen
- Flight Controls
Electricity
- Electricity is the set of physical phenomena associated with the presence and flow of electric charge.
- Wide known of electrical effects such as:
- Lightning
- Static electricity
- Electromagnetic induction
- Flow of electrical current
- Electricity permits the creation and reception of electromagnetic radiation as radio waves.
Electricity cont'd
Electricity occurs due to several types of physics:
- Electric charge
- Electric current
- Electric field
- Electric potential
- Electromagnets
Electricity cont'd
Electric Circuits
Electric Circuits
- An electronic circuit is composed of individual electronic components:
- resistors
- transistors
- capacitors
- inductors and diodes
- The combination of components and wires allows various simple and complex operations to be performed:
- signals can be amplified
- computations can be performed
- data can be moved from one place to another
Electric Circuits cont'd
- Circuits can be constructed of discrete components connected by individual pieces of wire
- However now more commonly a printed circuit board PCB by photolithographic techniques laminated substrate and attach the components to these connections to finish the circuit.
- Components in a circuit can be connected in many different ways. The 2 simplest ways:
- Series
- Parallel
Series
- Components connected in series are connected along a single path.
- So the same current flows through all of the components.
- Series circuits are sometimes called current coupled or daisy chain coupled.
- The current in a series circuit goes through every component in the circuit.
- Therefore, all of the components in a series connection carry the same current. There is only one path in a series circuit in which the current can flow.
- opening or breaking a series circuit at any point causes the entire circuit to open or stop operating.
Series
Parallel
- Components connected in parallel are connected so the same voltage is applied to each component.
- If two or more components are connected in parallel they have the same potential difference (voltage) across their ends.
- The potential difference is the same magnitude and the polarities are identical
- The same voltage is applicable to all circuit components connected in parallel.
- The total current is the sum of the currents through the individual components.
Parallel
Aircraft Electrical Systems
Aircraft Electrical Systems
- An Aircraft Electrical System is a self-contained network of components that:
- generate
- transmit
- distribute
- utilize
- store electrical energy
- Electrical systems vary in capacity and complexity between jet aircraft and piston aircraft. However, they share many of the same basic components.
Aircraft Electrical Systems cont'd
- All aircraft electrical systems have components with the ability to generate electricity.
- Depending upon the aircraft, generators or alternators are used to produce electricity. These are generally engine driven but may also be powered by an APU, a hydraulic motor or a Ram Air Turbine (RAT). Generator output is normally 115-120V/400HZ AC, 28V DC or 14V DC.
- Power from the generator may be used without modification or it may be routed through transformers, rectifiers or inverters to change the voltage or type of current.
Basic Systems
- Some very simple single engine aircraft do not have an electrical system installed.
- The piston engine is equipped with a Magneto ignition system which is self-powering and the fuel tank is situated so it will gravity feed the engine.
- If an electric starter, lights, electric flight instruments, navigation aids or radios are desired, an electrical system becomes a necessity.
- In most cases, the system will be DC powered using a single distribution bus, a single battery and a single engine driven generator or alternator.
- Provisions, in the form of an on/off switch, will be incorporated to allow the battery to be isolated from the bus and for the generator/alternator to be isolated from the bus.
Basic Systems
Basic Systems cont'd
- An ammeter, load meter or warning light will also be incorporated to provide an indication of charging system failure.
- Electrical components will be wired to the bus-bar incorporating either circuit breakers or fuses for circuit protection.
- Provisions may be provided to allow an external power source such as an extra battery or a Ground Power Unit to be connected to assist with the engine start or to provide power whilst the engine is not running.
Basic Systems cont'd
Electricity Backups and Defenses
- Multiple layers of redundancy greatly reduce the potential for loss of all electrical generation capability.
- Multiple primary generators and, where applicable, secondary (APU) or tertiary (RAT) generator installation.
- Components connected to the bus have individual circuit protection which, in the event of a component failure protect the bus from overload and thus protect the remaining components.
Electricity Backups and Defenses cont'd
- A bus failure is more typically the result of a failure of the power source supplying the bus and not the failure of the bus itself.
- Circuit breakers (CB) exist to protect the system from overload in the event of a component failure and to prevent a potential fire from developing in the component itself by interrupting the electrical supply.
- In the event a circuit breaker "pops" in flight, the crew should comply with manufacturer and company policy when deciding whether or not the CB should be reset.
- Should a reset CB pop a second time, further reset should NOT be attempted.
Magneto System
- Although the magneto system can pose a potential safety problem for those turning the propeller, its biggest advantage is that it provides an independent electrical system to keep the aircraft running until the magneto system itself fails or the fuel is exhausted or the engine stops running.
- To reduce the probability of a magneto failure, modern piston engines have dual or two separate magneto systems firing two separate spark plugs in each cylinder.
- Although both systems are normally used together, in the case of a magneto failure, one system is adequate to fly the aircraft to an airport where repairs can be made to the broken system.
Magneto Systems
Magneto System cont'd
- The important thing to remember is that a piston-powered aircraft engine does not need an alternator- or generator-based electrical system or battery to fly. This is an important safety point.
- Then why have an alternator or generator and battery in an aircraft?
Magneto System cont'd